With the rise and continuous improvement of the solid state lighting technology, due to properties such as high efficiency, energy saving, long lifetime and environment friendliness, the light emitting diode (LED) has become a preferable solution in the lighting engineering nowadays, and has been gradually applied in lighting products. A key factor which encourages people to focus on the LED lighting technology is that it significantly reduces the energy consumption and can realize long-term reliable operation.
The LED tube is drived by a DC power, and thus regardless of powering using the AC mains, the CCG or the ECG, a power adapter, that is, a LED driving circuit, is required to be added between the AC mains, the CCG or the ECG and the LED. The function of the LED driving circuit is to convert the supplied power to the DC power suitable for the LED.
The AC mains and the CCG can be approximately considered as low frequency constant voltage sources (a RMS value of an output voltage thereof is constant), while the ECG can be approximately considered as a high frequency constant current source (a RMS value of an output current thereof is constant). Since the ECG has different current and voltage output characteristics from the AC mains and the CCG, more and more attention has been paid to a design of a LED driving circuit which is compatible with the AC mains, the CCG and the ECG.
Currently, in the prior art, a driving circuit having two-stage converter of a boost type power factor correction (PFC) converter and a buck converter is used so as to be compatible with the AC mains, the CCG and the ECG, but the driving circuit using two-stage converter has a low working efficiency and a high cost. In this case, a design of a driving circuit having a single stage converter so as to be compatible with the AC mains, the CCG and the ECG has become a hotspot of interest.